Spoofing refers to impersonation by a hacker of another website or device on a network. They will often pick a device or website that you trust, which means that you are more likely to divulge sensitive information without raising an eyebrow. Usually, spoofing involves emails, IPs and DNS.
The only way to spot spoofing is by being very keen. If you get an email from a source you trust, but the email asks for very sensitive information, you need to be very wary before you respond. The same also goes for websites that you trust-if the site starts behaving strangely, then you need to be on your guard. Make use of quality software to protect your information as well.